How is a species defined?

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Carter Broach

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How is a species defined?
« on: 18/09/2008 10:45:35 »
Carter Broach asked the Naked Scientists:

The October issue of National Geographic magazine reported that scientists had claimed to identify about 2% of the DNA for Neanderthals, remarking that the difference between Neanderthals & modern humans is less than ½ of 1% of the entire sequence of the respective DNAs.  

Yet, Neanderthals are considered a different species than humans.  What criteria are used to claim that an animal, or plant, is a different species?

What do you think?


Offline Evie

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How is a species defined?
« Reply #1 on: 19/09/2008 15:17:38 »
Currently, the most basic determintation of species are organisms capable of interbreeding (and that naturaly do so in the wild) and producing fertile offspring. Creatures like ligers (tiger and lion cross) are produced only in captivity through human action.

Classification becomes problematic for extinct species, though, since we cannot determine whether or not they interbred. At that point, it becomes a bit more of a comparison game. Physiological differences, geographic isolation, etc. are then used to differentiate species, but such classifications are always under review and can change quite often.

The use of genetics is a bit of a double-edged sword right now. On a personal note, I was involved in the study of pallid sturgeon last summer, which are an endangered species of fish. They are capapble of breeding with shovelnose sturgeon, a close relative but seperate species in the current classification system. Some scientisits believe (based on genetic testing) that most pallid sturgeon currently in the Missouri River are actually a cross-breed with shovelnose. If there are no pure pallids left, then there's no reason to have them on the endangered list and throw lots of money into study and reclamation. There go a couple of hundred jobs, at least!

At some point, we may change the definition of species to incorporate genetic variation, though that would still be difficult for fossils, since they very rarely retain their own genetic material.

Wikipedia has a pretty long article going into much greater detail:
"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
Act I, scene 5